backend: ALWAYS provide a 'content' item in the JSON response, even when grave errors occur.  Previously, this was coded into modify_json4exception(), but (a) that code was removed in commit 3a57852f3db92426b466, and (b) that code inside modify_etc was never invoked anyway.
backend: ALWAYS provide a 'content' item in the JSON response, even when grave errors occur.  Previously, this was coded into modify_json4exception(), but (a) that code was removed in commit 3a57852f3db92426b466, and (b) that code inside modify_etc was never invoked anyway.

cpojer/mootools-filemanager,cpojer/mootools-filemanager